The general objective of this project is to evaluate the effects of changes in the temporal parameters of chromatic stimuli upon the middle-and long-wavelength color vision mechanisms of normal and color defective humans. Specifically, psychophysical measures of the increment and exchange thresholds, and Rayleigh matches will be used to determine the spectral sensitivity of human color vision under conditions in which the waveform, frequency, modulation amplitude and duty cycle of chromatic stimuli are varied.